I don't want to rain on the parade – especially a parade that I look forward to as much as this, that comes around comparatively rarely – but, speaking on behalf of all of us who've been lined up waiting in the cold and rain, I do have to register a slight… It's not a complaint exactly, I just want to let the organisers know that we know that parts of this parade have been around the block before. Faber published Lorrie Moore's The Collected Stories in 2008. To lure in fans like myself who owned and loved the earlier incremental volumes there was the inducement of three recentish stories from the New Yorker. Those stories turn up again here so that the tail, if not wagging, has somehow preceded the dog. That's three stories out of eight, or 63 pages out of 160, about 40% of the total: in doggy terms, not just the tail but a good bit of the hindquarters too.

The good news, mathematically speaking, is that the stories are pretty much 100% brilliant, as usual. There's not a dud among them. And I guess there's an underlying aesthetic and emotional unity here, something subtly distinct from her previous nest of new stories, 1998's Birds of America. That unity is emphasised by three dog-related epigraphs from poems, to which I would add a fourth from Billy Collins's The Revenant, in which a dog, having been put euphemistically to sleep, comes back from the dead to tell his master just one thing: "I never liked you." Crucial to this devastating revelation is the master's deluded assumption that he is not just liked or even loved but is the sun around which the dog's life orbits.

Anyone over the age of 16 knows that the human versions of the dogly virtues of loyalty, love and faithfulness can turn into their opposites so quickly as to make it seem that they exist primarily to facilitate the defining adult experiences of disillusionment and betrayal. The genius of Lorrie's Moore-ish take on the way our lives circle around and collide into others is to find constellations of relationships which reveal, very clearly, how hard these qualities are to distinguish from each other in the first place. Or, for that matter, how hard it is to tell first from last. Especially in a story like Subject to Search, which shuffles chronology so that the "happy ending" of the closing words actually takes place years before the rather desperate scene at its heart.

A similar irresolution is extensively choreographed in Wings, a tale of genuine May-December friendship between KC and Milt – and a rather suspect May-May romance between KC and her loser boyfriend, Dench. That it's a horror story, too, is brought out by the discovery, midway through, of something emblematically vile, but other details are innocently ominous too, from a takeaway coffee in "its warted brown vest" to the new urban dad, "so old he looked like the kidnapper of his own child". Ancient Milt himself, with his tea-stained sepia smile – "a dental x-ray from the 19th century" – and liver spots like a giraffe's, is foolish, fond and creepy in equal measure. He used to have an aptitude for German philosophy, the gist of which, he tells KC, is "Terrible world. Great sky." In less Hegelian, more nuanced terms, this means that the banana-flavoured custard he's ordered "doesn't taste like real banana but more like what burped banana tastes like".

That, her critics allege, could stand as an exquisitely distasteful illustration of Moore's basic recipe for fiction: a repeated reliance on overheard scraps and regurgitated gags in lieu of the nutritious full-bodied storytelling regularly ordered up by readers hungry for three-course novels. But, shifting focus from the content and substance to how it's served, bear in mind the words of one of her protagonists who reminds us that while this is an age of disposables, it's "also an age of fantastic adhesives." In a broken world, Moore has found a way of rendering the disposable indispensable, of making her stories and their brittle truths stick. These truths are enacted as subtly and emphatically as in any fiction – with the added virtue of brevity thrown in. Since the stories are also, as always, extremely funny, Moore has come to enjoy the unusual distinction of being just about the darkest light writer around. Unhappiness, heartbreak, illness, grief, disappointment – who'd have thought they could be so much fun? Or that fun could be so funereal?

Anyone seeking to answer these questions will return to the earliest stories in order to pose two more. Were traces of this gloom and sombreness already present amid the wry fizz and giggles of her first collection, Self-Help? And, relatedly, was there anything there that hinted at the longevity of an extended literary career, that she would be in it for the long haul? What I am struck by is how, aside from the expected maturing of tone and the enlarged range of experience on which she draws, the pleasures of reading Moore (and it is pretty much pure pleasure) have remained essentially the same. If she still seems a writer of enormous promise that is because promise – as embodied by the youthful daughters, the gorgeous and often gormless young who illuminate the middle-aged world of the recent stories – is still her subject, even if at least half of her attention is now fixed on its busted aftermath, when those fantastic adhesives are both badly needed and impediments to getting unstuck and moving on.

The means by which this is achieved is – to revert to an earlier set of metaphors – the lucid telescopic bonding of imagination and observation, the ability to zoom in on details so telling they resist certainties of interpretation: "She could see the creamy yellow of his teeth, his molars with their mercury eyes." Such moments are, as KC realises, "the very electricity of the real". And they are matched, in transient intensity of magnification, by atmospheric clarity: "Now the air was filled with the old-silver-jewellery smell of oncoming rain." Another story, about a couple's marital breakdown, is bathed in "the anxious conjugal dusk that was now their only life together". It's as sad, in its way, as the Larkin compromise in Talking in Bed – the difficulty of finding words "not untrue and not unkind" – but, for Moore, it's not a conclusion, just a transition to what will probably end up as a joke. Which in turn will become a trap door. What looks like a punchline is often a set-up for the killer counter-punch. If you're suicidal, a character points out, "and don't actually kill yourself, you become known as 'wry'". So you see, it was there in Self-Help: it just didn't yet know quite what it was.

All of which leads to a conclusion so surprising it sounds preposterous: that in her mid-50s Lorrie Moore is still a promising writer. It's possible, if nothing goes awry, that she will not hit her peak till her 70s. What a peak that's going to be: what depths she will be able to plumb when she gets there.

Geoff Dyer's new book, Another Great Day at Sea, will be published in May.